[R] Create a data frame of all possible unique combinations of factors

[jim holtman]

Is this what you want:

>  test <- c("A","B","C","D")
> expand.grid(test,test)
   Var1 Var2
1     A    A
2     B    A
3     C    A
4     D    A
5     A    B
6     B    B
7     C    B
8     D    B
9     A    C
10    B    C
11    C    C
12    D    C
13    A    D
14    B    D
15    C    D
16    D    D


On Tue, Jul 5, 2011 at 7:16 PM, Q <quagaars at gmail.com> wrote:
> Hello,
>
> I'm trying to create a data frame where each row has a unique combination of
> factors.
>
> I start with a vector of species like so:
>
>
>
>> 1> test <- c("A","B","C","D")
>>
>
>> 1> test
>>
>
>> [1] "A" "B" "C" "D"
>>
>
> To get all species combinations I have used expand.grid like this:
>
>
>
>> 1> pairs <- expand.grid(test,test)
>
>> 1> pairs
>
>>    Var1 Var2
>
>> 1     A    A
>
>> 2     B    A
>
>> 3     C    A
>
>> 4     D    A
>
>> 5     A    B
>
>> 6     B    B
>
>> 7     C    B
>
>> 8     D    B
>
>> 9     A    C
>
>> 10    B    C
>
>> 11    C    C
>
>> 12    D    C
>
>> 13    A    D
>
>> 14    B    D
>
>> 15    C    D
>
>> 16    D    D
>>
>
> Now I want to select only the unique pairs, which I have tried to do with
> the function "unique":
>
>
>
>> 1> unique(pairs)
>>
>
> , but that doesn't do anything... I guess because it considers A,B to be
> different from B,A.  The data frame I would like to end up with should look
> like this.
>
>
>
>>    Var1 Var2
>
>> 1     A    A
>
>> 2     B    A
>
>> 3     C    A
>
>> 4     D    A
>
>> 6     B    B
>
>> 7     C    B
>
>> 8     D    B
>
>> 11    C    C
>
>> 12    D    C
>
>> 16    D    D
>
>>
>
> Thanks for your help!
>
> Q
>
> --
> View this message in context: http://r.789695.n4.nabble.com/Create-a-data-frame-of-all-possible-unique-combinations-of-factors-tp3647338p3647338.html
> Sent from the R help mailing list archive at Nabble.com.
>        [[alternative HTML version deleted]]
>
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>



-- 
Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?